I was shooting the **** with my DSM buddy, and we were discussing intercooler piping diameters on his upcoming FMIC project. I then hit upon a question neither of us could explain or answer

Why is the i/c piping diameter smaller before the intercooler, then larger after? My convential reasoning suggests this is backwards - heated air takes up more space, cooler air less. Thus, you would need smaller piping after the intercooler to maintain velocity.

Obviously, my thinking is incorrect, because everyone does it this way. But, who can explain to me why?

 

nobody knows?!?! I'm surprised!

 

Why dont you try increasing the diameter of the intake and see what happens. Maybe you want to increase the flow to get to the intercooler then slow it down with the bigger piping for the cooler denser charge. I'm just talkin out my butt, not really sure..

 

I believe the main reason is that the discharge from the compressor is typically small; under 2" ID. If you connect that directly to a 3" or even 2.5" pipe, the rapid diffusion will make the air lose a tremendous amount of velocity and create a pressure rise, which will effectively make the turbo compressor fight against backpressure. Once it hits the IC, it's going to have to diffuse anyway, so they keep the flow small before the IC, then once it's diffused across the whole IC they can connect whatever size pipe they want. The concept bears some further exploration though... I wonder if I could put some temperature/density corrections onto the HVAC ducting spreadsheet I built here at work and check it out from a flow/pressure perspective.

Where's that CFD software when I need it?

 

I think mr dbman hit it on the nose. You want to keep the velocity up after the turbo outlet then you want the volume after the IC. Mr. dbman, do you have any work for an AC guy of 8 years? Turbos and ACs go hand in hand.......

 

Well I would have thought because hot air travels faster than cold air. Remeber hot air expands kinda like a hot air ballon so you have a force pushing force, then it gets cool with the IC making it dense and more air.
Hot air= less air but travels fast and expands.
Cool air= more air and cool for combustion.

I guess, but I really dont know. Im just trying to brainstorm. Its making my head hurt...lol


art

 

G, I'm a recently graduated mechanical engineer; I've been doing some HVAC stuff for the company I just started working for, so all that ductwork pressure drop stuff was at the top of my head. Is your background in AC installation work or in the engineering/design side of it?

 

ah ha, that makes sense, thanks guys

 

this question has been bothering me since it was posted, so like I do with everything I researched it.
Ok, lets use something we can compare it to. The air in your lungs are warm. If you blow on your arm with your mouth wide open the air feels warm. But, if you pucker your lips and blow on your arm the air feels cool. why does this happen?
When you blow on your arm with mouth wide open, you get a gush of warm air as indicated by our temp. sense. However, when you blow with your lips puckered, the stream of air is compressed kinda like a turbo. Then, as it emerges, the air expands, doing work against the atmosphere. This work is done at the expense of the internal energy of the air, so the temp of the air is decreased and it feels cooler. This takes place quickly and is a "quasi-adiabatic" process.

So, not only does the IC's heat sinks used to cool the intake charge but it cools it by expanding the heat air coming out of the compressor. Then the piping is also bigger. So that my friend is the best thing I could find.

art

 

interesting Art, never thought about it that way.